In general, capacitive touch sensors are intended to replace mechanical buttons, knobs, and other similar mechanical user interface controls. Capacitive sensors allow the elimination of complicated mechanical switches and buttons and provide reliable operation under harsh conditions. Also, capacitive sensors are widely used in modern consumer applications, providing new user interface options in the existing products.
The capacitance detected by a capacitive sensor changes as a function of the proximity of a conductive object to the sensor. The conductive object can be, for example, a stylus or a user's finger. In a touch-sensor device, a change in capacitance of the sensor array due to the proximity or movement of a conductive object can be measured by a variety of methods. Regardless of the method, usually an electrical signal representative of the capacitance detected by each capacitive sensor is processed by a processing device.
FIG. 1 illustrates a layout for conductive traces in a conventional capacitive sensor having five touch-sensor buttons. Capacitive sensor 100 includes button 101, button 102, button 103, button 104, and button 105, which correspond to button locations 1, 2, 3, 4, and 5, respectively. These buttons may be capacitive touch-sensor buttons and may be used for user input using a conductive object, such as a finger or stylus. For example, each of the five button locations may be assigned to a different function so that when an input is detected at one button location, the processing device detecting the input performs the function associated with that button location. In a capacitive sensor having five buttons, such as capacitive sensor 100, a processing device connected to the sensor may be required to monitor five different capacitance signals, one capacitance signal for each button location, in order to determine whether and when an input has been received at any one of the button locations.